Abstract
Anaplastic large cell lymphoma (ALCL) comprises a group of T-cell non-Hodgkin lymphomas unified by common morphologic and immunophenotypic characteristics, but with a spectrum of clinical presentations and behaviors. Early identification of anaplastic lymphoma kinase (ALK) gene rearrangements in some ALCLs led to recognition of ALK as an important diagnostic and prognostic biomarker, and a key driver of ALCL pathobiology. Rearrangements and other genetic abnormalities of ALK subsequently were identified in diverse other human malignancies. Recent clinical, pathologic, and genetic data have begun to shed light on ALK-negative ALCLs, revealing significant heterogeneity within this more ill-defined entity.